The present invention is directed to real time and off line signal processing of a signal indicating plasma concentration within a processing chamber.
In a processing chamber, for example an etch chamber used for performing a reactive ion etch, the concentration of plasma within the processing chamber is monitored to determine the end point of the process. Since the light intensity from the flow of the plasma is proportional to the concentration of plasma within the processing chamber, the light intensity within the processing chamber is monitored using a photo multiplier tube (PMT). The PMT generates an electrical signal with a voltage which is proportional to the light intensity. This signal is amplified and forwarded to a computer. The computer uses the signal to look for certain parameters in order to intervene in the process, e.g., to determine the end point of the process, when processing is to be stopped.
When a rotating magnetic field is used in the processing chamber, this causes plasma in the processing chamber to circulate. The circulation of plasma causes significant variations in the light intensity measured by the PMT. In order to accurately determine the end point of the process, the computer needs to filter the signal from the PMT to remove the noise caused by effects of the circulation. It is desirable to generate a display to a user which represents the method by which the computer determines the end point of the process.